U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Apparent Solute Dispersion in an Alluvial/Aquifer Stream System

Abstract

In simulations of solute transport, the dispersion coefficient characterizes the spreading and mixing of the solute due to variations in ground-water flow velocity that are not explicitly included in the simulation. Although usually considered to be the result of variability in hydraulic conductivity, dispersion also can result from variations in the direction of ground-water flow. A computer simulation of ground-water flow and solute transport in an alluvial aquifer/stream system shows that fluctuations in river stage and subsequent changes in the direction of ground-water flow in the aquifer cause an increase in apparent dispersion. Solute plumes in an alluvial aquifer near a river move more slowly and become more dilute as a result of ground-water/surface-water interaction than if this interaction were not considered.